Medical diagnostic x-ray equipment has long used x-ray film contained inside a lightproof cassette, with the cassette at one side of the patient and an x-ray source at the opposite side. During exposure, x-rays penetrate the desired body location and the x-ray film records the spatially varying x-ray exposure at the film. Over the years, medical experience has developed and optimized a variety of standard protocols for imaging various parts of the body, which require placing the film cassette in different positions relative to the patient. Chest x-rays, for example, are often performed with the patient standing, chest or back pressed against a vertical film cassette. Imaging of the bones in the hand might be done with the cassette placed horizontally on a surface, and the hand placed on top of the cassette. In another procedure the patient might cradle the cassette under an arm. A collection of such standard protocols is described in Merrill's Atlas of Radiographic Positions and Radiologic Procedures, by Philip W. Ballinger, et. al., 9th edition, published by Mosby-Year Book, Incorporated, hereby incorporated by reference.
Advances in digital x-ray sensor technology have resulted in the development of arrays of sensors that generate electrical signals related to local x-ray exposure, eliminating film as the recording medium. An example is discussed in U.S. Pat. No. 5,319,206, incorporated herein by reference, and a current version has been commercially available from the assignee of this patent specification. Such digital arrays are often called flat panel x-ray detectors, or simply flat panel detectors, and offer certain advantages relative to x-ray film. There is no need for film processing, as the image is created and comes from the cassette in electronic digital form, and can be transferred directly into a computer. The digital format of the x-ray data facilitates incorporating the image into a hospital's archiving system. The digital flat panel detectors or plates also offer improved dynamic range relative to x-ray film, and can thus overcome the exposure range limitations of x-ray film that can necessitate multiple images to be taken of the same anatomy. On the other hand, digital flat panel detectors currently have a higher capital cost than film cassettes, and are more fragile. They often incorporate lead shielding to protect radiation-sensitive electronics, and can be heavy. If they are connected to a computer with a cable, cable handling needs to be taken into consideration when moving the cassette and/or the patient. Alternatively, the cassette can be self-contained, as for example in U.S. Pat. No. 5,661,309, in which case it includes a power supply and storage for the image information, increasing its weight and possibly size. Such detectors commonly are used in a system comprising a suitable anti-scatter or Bucky plate.
The high initial cost of the digital detector can hinder outfitting of an x-ray room with multiple detectors pre-mounted in a variety of positions, such as a vertically-mounted unit for chest, and a horizontal unit under a bed. The fragility, weight, and initial cost of the units make them difficult to use in procedures where the patient cradles the detector. The unique characteristics of digital flat panel detectors can make conventional film cassette holders impractical for use with flat panel detectors.
A number of proposals have been made for x-ray systems using flat panel detectors. A C-arm arrangement has been offered under the name Traumex by Fisher Imaging Corporation of Denver, Colo., with the participation of a subsidiary of the assignee hereof. Another C-arm arrangement is believed to be offered under the name ddRMulti-System by Swissray, and literature from Swissray has stated that a ddRCombi-System is scheduled for launch in early 2000 and would offer the same functionality as the ddRMulti-System but would use existing third party suspension equipment for the x-ray tube (an illustration therein appears to illustrate a detector arrangement mounted for vertical movement on a structure separate from a ceiling-mounted x-ray tube support. A vertically moving and rotating image intensifier appears to be illustrated in FIG. 3 of U.S. Pat. No. 4,741,014. U.S. Pat. Nos. 5,764,724 and 6,155,713 propose other configurations.
A number of other proposals have been made for positioning x-ray film cassettes but the different physical characteristics and requirements of flat panel detectors systems do not allow for direct application of film cassette positioning proposals. For example, U.S. Pat. No. 4,365,344 proposes a system for placing a film cassette in a variety of positions and orientations relative to a floor mounted x-ray source support. U.S. Pat. No. 5,157,707 proposes moving a film cassette to different positions relative to a ceiling mounted x-ray tube support to allow taking AP (anterior-posterior) and lateral chest images of a patient sitting on a bed. The figures of Swedish patent document (Utlaggningsskrift [B]) 463237 (application 8900580-5) appear to show a similar proposal as well as a proposal to mount the x-ray cassette and the x-ray source on the same structure extending up from the floor. U.S. Pat. 4,468,803 proposes clamping an articulated support for a film cassette on a patient table, and U.S. Pat. No. 5,920,606 proposes a platform on which a patient can step and into which a film cassette can be inserted to image a weight-bearing foot.
With a view to the unique characteristics and requirements of digital flat panel detector systems, it is believed that a need exists to provide a safe, reliable, convenient and effective way to position such systems for a wide variety of imaging protocols, and this patent specification is directed to meeting such a need.